Director James Gray wrote to Francis Ford Coppola, who directed Apocalypse Now (1979), asking for advice about shooting in the jungle. Coppola's two-word reply was "Don't go." Coppola had received the same advice from Roger Corman.
Shooting on 35mm film posed significant logistical challenges in the middle of the Colombian jungle. "It was an act of absolute hubris to shoot this picture on film," said James Gray, who set up an elaborate routine to ship, process, and review the film during production. "First, we had to teach a young guy from Bogotà how to load the film, because nobody really knows how to do that anymore Then, every day after we finished our shoot, they'd put this film into a torn-up crappy cardboard box and load it onto a single-engine crop duster that would take off from this little runway. You're talking three flights every day just to get your film processed. The next morning, there was always this sense of dread when the satellite phone rang and you'd be thinking, 'I really hope the film arrived.'"
While filming in the jungle, Hunnam remembers a particularly nerve-wracking encounter one Saturday night following an exhausting six-day shooting week. "I was staying in this little shack on this hill and woke up at three in the morning to this ungodly noise, like there was a pneumatic drill in my ear. An insect had burrowed into my ear and hit my eardrum so it couldn't go any further. It was a long beetle with wings. When it couldn't get back out, it kept trying to burrow further in and flapping its wings. That's what woke me up."
Tom Holland inadvertently went swimming with the largest predators in the Amazon basin. "I got in the river one day with the local kids and had the best day ever, but I didn't realize the water was filled with black caimans, which are like giant alligators," he says. "The next day we were filming on the boat when I saw this big crocodile-looking thing in the river. Apparently they are very docile and don't really attack people, but to me this thing looked as mean as could be."
Most of Pattinson's scenes took place in uncomfortable situations in the jungle, where he forged a close rapport with Hunnam. "Charlie and I would be an hour up river from the base camp basically covered in sand fleas all day," Pattinson says. "It's definitely a bonding experience when there's no way to hide from extreme conditions. I remember we pushed a wooden raft with horses on it upstream. After just one day of that, you're completely done, yet the real guys did this for three years every single day, going against the river. It's complete madness."